Jeb Bush’s plunge into presidential waters — few politicians “actively explore” a White House run without knowing where those explorations will lead — ends some uncertainties about the 2016 campaign and creates others.

It gives shape to the Republican campaign and, if Mr. Bush prevails and if Hillary Rodham Clinton wins the Democratic nomination, sets up an epic dynastic struggle. It accelerates the pace of the Republican race — no one thought Mr. Bush would make a decision before Christmas in the year of the midterm congressional contests — and puts pressure on other potential contenders to claim donors and build an operational base.

The Republican race now is the mirror image of the Democratic race, with one brand-name candidate and a clutch of relative unknowns maneuvering for position and attention. It has taken Ted Cruz of Texas, Marco Rubio of Florida and Rand Paul of Kentucky, all first-term senators, months of exhausting efforts to attract a fraction of the name recognition or national political appeal that Mr. Bush possessed even before last week’s announcement.

Still, there is no guarantee Mr. Bush will be nominated, and at least a handful of Bush watchers caution that the former Florida governor is independent enough to break form and walk away from the race once it’s been explored.

Moreover, the past is full of appealing figures who seemed poised to reshape presidential campaigns but proved to be duds on the national stage — Govs. George W. Romney of Michigan and Pete Wilson of California along with former Sen. Fred Thompson on the Republican side, Sens. Edmund S. Muskie of Maine and Bill Bradley of New Jersey on the Democratic side. Not one of them reached even the second phase of the campaigns they were expected to dominate.

But the real importance of the Bush announcement is that it prompts a series of important conflicts. Among them:

• Insurgents vs. the establishment. This tension always was going to be a major feature of the 2016 campaign, but the presence of a Bush — one of two 1990s Bush governors, the son and brother of a president, the grandson of a patrician senator and the great-grandson of the man for whom golf’s coveted Walker Cup is named — clearly defines it as a contest about the character of the Republican Party.

The campaign now will be a struggle between creation narratives, with Messrs. Cruz and Rubio speaking of their immigrant heritages and Mr. Bush implicitly representing the moderate northeastern wing of the GOP, even though he was born and reared in Texas and is a graduate not of Yale but of the University of Texas, where he took a degree in Latin American studies, was named to Phi Beta Kappa and graduated in less than three years.

• New face vs. dynasty. This is less a factor if Mrs. Clinton emerges swiftly as the consensus Democratic nominee, though a second Clinton-Bush contest, an unsettling echo of 1992, would be hard to explain to Third World nations that Americans routinely scold for their dynastic politics.

It could be possible to say in 2016 that a Bush or a Clinton was on a national ticket in every American election but two for 36 years. That prospect alone may undermine Mr. Bush’s appeal and fuel Republican desires for a new face.

• Ripples from Bush 41 or of Bush 43? For months Democrats have been peddling the notion that no one could conceivably support another Bush presidency in the wake of the disasters they believe George W. Bush perpetrated while in the White House. A Quinnipiac University poll taken six months ago found that more than a quarter of Americans thought the younger Mr. Bush was the worst president of the postwar era.

But there was another President Bush, and in the past two decades the father has emerged as one of the most beloved figures on the American scene — a wise man and a gentleman. In the younger President Bush’s memoir about his father, which was published this autumn and carries the title “41,” he wrote about being asked in his 2000 campaign about what effect the first President Bush would have on his campaign. “I joked,” he wrote, “that I had inherited half of his friends and all of his enemies.” Today the number of Bush 41 friends has more than doubled, and the number of his enemies has virtually disappeared.

• Above the fray or amid the fray? Mr. Bush has indicated skepticism about the scrum that modern presidential politics has become. He won’t be able to stay above it for long. That presents perhaps the biggest challenge to the Bush campaign.

Mr. Bush has made minimal gestures of outreach to operatives in the early political states. Besides transit through New Hampshire en route to his family’s vacation retreat in coastal Maine, Mr. Bush has basically not visited the state with the first presidential primary for 14 years. He has spoken to none of the important Republican political figures there. His father and brother have stronger roots in the state than he has, even though his center-right political profile is better suited to New Hampshire than to Iowa, which holds the first caucuses.

All that speaks to the Bush style, version 3.0. He is insular, keeping a very tight circle around him: basically Alberto Cardenas, chairman of the American Conservative Union and a top Washington lobbyist, and Mel Sembler, former American ambassador to Australia (appointed by 41) and Italy (appointed by 43) and a prodigious fundraiser — a marked contrast to the Clinton 2008 entourage, an all-star roster of feuding consultants.

His father’s style was based on relationships and consensus. His brother’s style was more visceral. Mr. Bush is the contemplative one among the three. Just short of wonkish, he studies issues even when he doesn’t have to, or isn’t pressed for a decision.

Jeb Bush is not interested in ending government but in making it more efficient. He’s a modern Republican, fluent in Spanish and in the argot of education, but he may be the most old-fashioned Republican in politics today. His campaign represents a struggle between two incompatible views of the Republican future, and of the country. The 2016 race didn’t just get more intense last week. It also got more interesting — and more important.

David Shribman, a Pulitzer Prize winner in journalism, is executive editor of the Pittsburgh Post-Gazette.